Thermostat controller

ABSTRACT

A refrigeration system ( 10 ) has a compressor ( 12 ), condensor ( 13 ) and evaporator ( 14 ) connected in a refrigeration circuit. A controller ( 16 ) has probes ( 19, 20 ) for sensing the temperatures of the evaporator ( 14 ) and condensor ( 13 ) respectively. The controller controls the operation of the compressor, and hence the refrigeration circuit, so that the compressor does not start unless the evaporator temperature is above a preselected value (T start ), and stops the compressor if the evaporator temperature falls below T disable . An alarm ( 21 ) is activated if the condensor temperature rises above T alarm , and the controller ( 16 ) stops the compressor ( 12 ) if the condensor temperature rises above a higher temperature T shutdown .

[0001] This invention relates to a method and apparatus for thermostat control of a refrigeration system. In particular, the invention is directed to an improved thermostat control method and apparatus in which the refrigeration mechanism is disabled in the event of abnormal temperatures in components of the refrigeration mechanism.

BACKGROUND ART

[0002] Refrigeration mechanisms, such as those used to refrigerate display cabinets, usually have a thermostat which maintains the temperature of the cabinet chamber at or near a desired temperature. The thermostat normally operates with a fixed hysteresis to avoid overly frequent switching of the refrigeration mechanism. That is, for a desired set temperature (T_(set)), the thermostat will activate the refrigeration mechanism when the temperature rises above a temperature (T_(max)) which is slightly above T_(set). The refrigeration mechanism will continue to operate until the temperature of the refrigerated space falls below a temperature (T_(min)) which is slightly below T_(set). The thermostat will not activate the refrigeration mechanism again until the temperature of the refrigerated space rises above T_(max).

[0003] In most refrigerated cabinets and similar refrigeration systems, the thermostat controls the refrigeration mechanism in response to one only of the following: the temperature of the refrigerated space, the temperature of the refrigerated product or the evaporator temperature.

[0004] It is an object of this invention to provide an improved thermostat controller which is responsive to one or more conditions in addition to the temperature of the space or product being cooled.

SUMMARY OF THE INVENTION

[0005] In one broad form, the invention provides a refrigeration system having:

[0006] a refrigeration mechanism for cooling an object, the refrigeration mechanism including a compressor, condensor and evaporator in a refrigeration circuit;

[0007] thermostat means for regulating the operation of the refrigeration mechanism in response to the temperature of the object;

[0008] wherein the refrigeration system further includes control means for controlling the refrigeration mechanism in response to the sensed temperature of at least one component of the refrigeration mechanism, the control means overriding the normal operation of the thermostat means.

[0009] The term “object” is used in a broad sense, and includes a space such as a refrigerator chamber, or one or more items or products within that chamber, or a container, or a liquid within the container.

[0010] Preferably, the control means controls the operation of the refrigeration mechanism in response to the temperature of the evaporator. In one embodiment, the control means stops or otherwise disables the operation of the refrigeration mechanism if the temperature of the evaporator drops below a predetermined temperature (T_(disable)). Further, the control means controls the refrigeration mechanism to ensure that it does not commence unless the temperature of the evaporator is above a (higher) pre-determined temperature (T_(start)).

[0011] The control means will therefore override the thermostat means and disable the refrigeration mechanism if the evaporator temperature falls below T_(disable). This may be caused by the evaporator icing up or, in the case of a forced draught system, failure of the evaporator fan(s). Further, the control means overrides the normal operation of the thermostat means to ensure that the refrigeration mechanism will only start if the evaporator is completely defrosted, i.e. the evaporator temperature is above T_(start). The control means therefore ensures that the refrigeration mechanism operates only when the evaporator is able to operate effectively.

[0012] The refrigeration system suitably includes a temperature probe connected to the control means and adapted to sense the temperature of the evaporator.

[0013] Further, or in the alternative, the control means controls the refrigeration mechanism in response to the temperature of the condensor. Typically, if the condenser temperature rises above a predetermined value (T_(alarm)), an alarm is triggered. The alarm may suitably be an audio and/or visual alarm. This alarm may be reset by switching the power off for a predetermined period, then switching it back on. However, the alarm will reactivate if the condenser temperature remains above T_(alarm).

[0014] If the condensor temperature rises above a (higher) predetermined valued (T_(shutdown)), the control means will stop or otherwise disable the refrigeration mechanism, until re-set in the same manner as the alarm.

[0015] By controlling the refrigeration mechanism in response to the condenser temperature, the control means ensures safe operation by alerting the operator to high condenser temperature and/or shutting down the refrigeration mechanism in the event of sustained high condensor temperature.

[0016] The refrigeration system may suitably include a temperature probe connected to the control means for sensing the temperature of the condensor, as well as an alarm circuit.

[0017] The control means may suitably be in the form of an electronic circuit which also incorporates the thermostat means. The electronic circuit may include a programmed micro-processor or any other suitable electrical control circuit.

[0018] In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram of the refrigeration system of the preferred embodiment;

[0020]FIG. 2 contains temperature and operational charts illustrating the operation of the refrigeration system in various conditions.

DESCRIPTION OF PREFERRED EMBODIMENT

[0021] As shown in FIG. 1, a refrigeration system 10 includes a conventional refrigeration mechanism 11 which comprises a compressor 12, condenser 13 and evaporator 14 connected in a refrigeration circuit. The evaporator 14 is typically used to cool a space 15 such as the product cabinet or chamber of a display refrigerator. However, the evaporator 14 may also be used to cool a product directly or indirectly.

[0022] The refrigeration system 10 also includes a thermostat controller 16 which incorporates the functions of a conventional thermostat and the control means of this invention. A temperature sensor or probe 17 located in the refrigerated space 15 is connected to an input of the thermostat controller 16. In its normal thermostat function, the thermostat controller switches the compressor 12 on and off so that the evaporator 14 maintains the refrigerated space 15 close to a pre-determined temperature (T_(set)) set by a temperature adjustment potentiometer 18, with typical hysteresis control. That is, when the temperature of space 15 as sensed by probe 17 rises above T_(max) (slightly above T_(set)), the compressor 12 is switched on so that the evaporator 12 cools the space 15. When the temperature of the space 15 falls below T_(min) (slightly below T_(set)), the compressor 12 is switched off. The abovedescribed temperature control procedure is well known, and need not be described in detail.

[0023] According to the preferred embodiment of this invention, the refrigeration system 10 further includes a temperature sensor or probe 19 connected to an input of the thermostat controller 16. The sensor 19 senses the evaporator temperature, and the thermostat controller controls the operation of the compressor 12 in response to that temperature overriding the conventional hysteresis thermostat operation described above.

[0024] More specifically, the temperature controller 16 will only activate the compressor 12 if the temperature of the evaporator is above a predetermined temperature, T_(start). At this temperature, the evaporator is completely defrosted. Hence, the thermostat controller will not start the compressor unless the evaporator is defrosted. If during operation, the temperature of the evaporator 14 falls below a (lower) pre-determined temperature T_(disable), the thermostat controller overrides the normal thermostat hysteresis operation, and stops or disables the compressor 12.

[0025] The temperature T_(disable) is selected as being a temperature which would be reached if, for example, the evaporator begins to ice up or, in the case of a forced draught system, there is a failure of the evaporator fan(s) thereby reducing the evaporators capacity to cool. Hence, the thermostat controller ensures that the refrigeration mechanism is shut off if the evaporator falls to a temperature which is too low to function effectively. Moreover, the thermostat controller 16 will not allow the compressor 12 to be restarted by the normal hysteresis thermostat unless the temperature of the evaporator has risen above T_(start).

[0026] The refrigeration system also includes a second temperature sensor or probe 20 connected to an input of the thermostat controller 16. The temperature sensor 20 senses the temperature of the condenser 13, and the controller 16 actuates an alarm 21 and/or controls the operation of the compressor 12 in response to that temperature (overriding the normal hysteresis thermostat operation).

[0027] If the condenser temperature, as sensed by sensor 20, rises above a pre-determined value T_(alarm), the controller 16 will activate an alarm 21. This is typically an audible alarm, such as a buzzer, but may be a visual alarm, such as a warning light. The alarm may be re-set by switching off the power to the refrigeration system for a pre-determined period of time, say 30 seconds, and then switching the power back on. However, if the condensor temperature is still above T_(alarm) the alarm 21 will remain activated. The temperature T_(alarm) is selected to indicate some overheating of the compressor.

[0028] If the condensor temperature 13 rises above a higher temperature T_(shutdown), the thermostat controller will override the normal thermostat hysteresis control of the compressor 12 and shut down or otherwise disable the compressor. The temperature T_(shutdown) is selected to be the maximum allowable operating temperature of the compressor. The refrigeration mechanism will remain shut down until re-set by switching the power on and off as for the alarm re-set. However, if the temperature is still above T_(shutdown), the refrigeration mechanism will remain disabled. This safety mechanism ensures that the refrigeration system is not operated if the condenser temperature is unduly high.

[0029] An example of the operation of the refrigeration system is illustrated in FIG. 2. At start up, if the temperature in the chamber 15 is above T_(max), and providing that the evaporator temperature is above T_(start), the compressor will be switched on by the controller 16. Once the chamber temperature has dropped below T_(min) (at T₁), the compressor will be switched off in accordance with the normal hysteresis control procedure.

[0030] At T₂, when the chamber temperature has risen above T_(max), and again providing that the evaporator temperature is above T_(start), the compressor will be switched on. However, if the evaporator temperature drops below T_(disable) (at T₃), the compressor will be switched off even though the chamber temperature has not yet reached T_(min). The compressor will not start again until the evaporator temperature rises above T_(start) (at T₄).

[0031] If the condenser temperature rises above T_(alarm) (at T₅), the alarm 21 will switch on, and remain on until the condensor temperature drops below T_(alarm) (at T₇) and is reset (at T₇) as described above. Further, if the condenser temperature rises above T_(shutdown) (T₆), the thermostat controller will override the normal hysteresis control, and shut down the compressor leaving the alarm on, until reset (T₇) as described above, typically after the temperature has dropped below T_(alarm). (In the illustrated example, although the condenser temperature no longer overrides the normal hysteresis control at T₇, the compressor does not switch on until the evaporator temperature rises above T_(start) (at T₈)). If the system is reset after the condensor temperature has dropped below T_(shutdown) but above T_(alarm), the compressor will normally start again but the alarm will sound.

[0032] The foregoing describes only one embodiment of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention.

[0033] For example, the refrigeration system may include a display panel to display the temperatures of the evaporator and/or condenser, or indicate when the temperatures of the evaporator and/or condenser are outside normal operating parameters. 

1. A refrigeration system having a refrigeration mechanism for cooling an object, the refrigeration mechanism including a compressor, condensor and evaporator in a refrigeration circuit, a thermostat means for regulating the operation of the refrigeration mechanism in response to the temperature of the object, and wherein the refrigeration system further includes control means for controlling the refrigeration mechanism in response to the temperature of at least one component of the refrigeration mechanism, the control means overriding the normal operation of the thermostat means.
 2. A refrigeration system as claimed in claim 1 , including a first sensor for sensing the temperature of the evaporator, the sensor being connected to the control means, wherein the control means is responsive to the sensed temperature of the evaporator to control the operation of the refrigeration mechanism.
 3. A refrigeration system as claimed in claim 2 , wherein the control means is responsive to the sensed evaporator temperature to stop operation of the refrigeration mechanism if the sensed evaporator temperature falls below a first predetermined temperature.
 4. A refrigeration system as claimed in claim 3 , wherein the control means is responsive to the sensed evaporator temperature to prevent commencement of operation of the refrigeration mechanism if the sensed evaporator temperature is below a second predetermined temperature, the second predetermined temperature being higher than the first predetermined temperature.
 5. A refrigeration system as claimed in claim 2 , including a second sensor for sensing the temperature of the condenser, the sensor being connected to the control means, wherein the control means is responsive to the sensed temperature of the condenser to control the operation of the refrigeration mechanism.
 6. A refrigeration system as claimed in claim 5 , further including an alarm, the alarm being activated by the control means if the sensed condensor temperature rises above a predetermined third temperature.
 7. A refrigeration system as claimed in claim 6 , wherein the control means is responsive to the sensed condensor temperature to disable operation of the refrigeration mechanism if the sensed condensor temperature rises above a predetermined fourth temperature.
 8. A refrigeration system as claimed in claim 1 , including a sensor for sensing the temperature of the condensor, the sensor being connected to the control means, wherein the control means is responsive to the sensed temperature of the condenser to control the operation of the refrigeration mechanism.
 9. A refrigeration system as claimed in claim 8 , further including an alarm, the alarm being activated by the control means if the sensed condensor temperature rises above a predetermined third temperature.
 10. A refrigeration system as claimed in claim 9 , wherein the control means is responsive to the sensed condensor temperature to disable operation of the refrigeration mechanism if the sensed condenser temperature rises above a predetermined fourth temperature.
 11. A refrigeration system as claimed in claim 1 , wherein the thermostat means and the control means are incorporated in an electronic control circuit.
 12. An electronic controller for a refrigeration system having a refrigeration mechanism for cooling an object, the refrigeration mechanism including a compressor, condenser and evaporator connected in a refrigeration circuit, the electronic controller including a thermostat for regulating the operation of the refrigeration circuit in response to the temperature of the object, at least one temperature sensor for sensing the temperature of at least one component of the refrigeration mechanism, and an electronic control circuit responsive to the sensed temperature of the component(s) for controlling the operation of the refrigeration mechanism, the electronic control circuit overriding the operation of the thermostat.
 13. An electronic controller as claimed in claim 12 , having a temperature sensor for sensing the temperature of the evaporator, the electronic control circuit being responsive to the evaporator temperature sensed by the sensor to disable operation of the refrigeration mechanism if the sensed evaporator temperature falls below a first predetermined value.
 14. An electronic controller as claimed in claim 12 , having a temperature sensor for sensing the temperature of the condenser, the electronic control circuit being responsive to the condensor temperature sensed by the sensor to disable operation of the refrigeration mechanism if the sensed condensor temperature rises above a second predetermined value.
 15. An electronic controller as claimed in claim 13 , having a second temperature sensor for sensing the temperature of the condenser, the electronic control circuit being responsive to the condensor temperature sensed by the second sensor to disable operation of the refrigeration mechanism if the sensed condenser temperature rises above a second predetermined value.
 16. A method of operating a refrigeration system having a refrigeration mechanism for cooling an object, the refrigeration mechanism including a compressor, condensor and evaporator connected in a refrigeration circuit, the method including the steps of using a thermostat to regulate the operation of the refrigeration mechanism in response to the temperature of the object, and overriding the normal operation of the thermostat and controlling the operation of the refrigeration mechanism in response to the sensed temperature of at least one component of the refrigeration mechanism.
 17. A method as claimed in claim 16 , wherein the operation of the refrigeration mechanism is controlled in response to the sensed temperature of the evaporator, including the step of disabling operation of the refrigeration mechanism if the sensed evaporator temperature falls below a first predetermined value.
 18. A method as claimed in claim 16 , wherein the operation of the refrigeration mechanism is controlled in response to the sensed temperature of the condenser, including the step of disabling operation of the refrigeration mechanism if the sensed condensor temperature rises above a second predetermined value.
 19. A method as claimed in claim 17 , wherein the operation of the refrigeration mechanism is also controlled in response to the sensed temperature of the condensor, including the step of disabling operation of the refrigeration mechanism if the sensed condenser temperature rises above a second predetermined value. 